Radiofrequency dielectric properties of animal tissues as a function of time following death.

The dielectric properties of three bovine tissues, liver, kidney and spleen, as a function of time following death, were measured in the frequency range from 20 kHz to 100 MHz using an automatic network analyser and an end-of-the-line sensor. The dielectric constant of kidney and spleen decreases as a function of time following death, particularly at frequencies below 1 MHz. However, all tissues measured show a characteristic increase in the frequency-independent ionic conductivity. This is believed to reflect changes in the conductivity of the extracellular region of tissues after death. The dielectric parameters, i.e. the static dielectric constant, the relaxation time and the coefficient of the relaxation time distribution, obtained by a curve-fitting process, do not change within the first 10 h following death in the case of liver, whereas early changes occur for both kidney and spleen. High initial values of the static dielectric constant for these tissues decrease significantly within a few hours following death. Similarly, the relaxation time which is relatively long for kidney and spleen, as compared with liver, decreases with time. Our data compare favourably with those reported by several investigators for similar tissues in other species (dog, cat, swine and cattle).